Several remain in camp competing for spots, others impressed before being sent down

The rosters are being trimmed regularly as Opening Day approaches. More and more prospects are being optioned or assigned with each passing day.

Some are still getting Grapefruit or Cactus League at-bats and innings because they are competing for spots on 25-man rosters. Others have made strong impressions and will undoubtedly be heard from again in the future.

Here's a list of prospects who have stood out this spring, either while fighting for a job or in making a strong impression, broken into those two categories (Prospect Watch rankings in parentheses; all statistics are through Thursday).

Still up and fighting

Nolan Arenado, 3B, Rockies (No. 62 on Top 100; No. 2 on Rockies' Top 20): Trying to unseat Chris Nelson and make a leap from Double-A, Arenado has hit well, with a .314 average and .743 slugging percentage. His four homers all came early in the spring.

Jackie Bradley Jr., OF, Red Sox (No. 32 on Top 100; No. 2 on Red Sox's Top 20): Injuries are making Bradley a viable Opening Day option, but even if everyone was healthy, hitting .444 with a 1.123 OPS in 45 at-bats has made for a strong case that he's ready for the highest level.

Travis d'Arnaud, C, Mets (No. 6 on Top 100; No. 1 on Mets' Top 20): d'Arnaud has made the most of his first Mets camp, hitting .333 over 30 at-bats with a pair of homers, while serving notice that John Buck is merely keeping the spot warm for him.

Khris Davis, OF, Brewers (No. 16 on Brewers' Top 20): Davis has continued to show the ability to swing a bat, hitting five homers to go along with a .317 average. He's below average defensively, but there's a chance he could stick on Milwaukee's Opening Day roster in a bench role.

Kevin Gausman, RHP, Orioles (No. 37 on Top 100; No. 2 on Orioles' Top 20): Dylan Bundy has been fine, but Gausman has drawn raves from scouts, striking out 14 batters in 12 1/3 innings.

Jedd Gyorko, 2B/3B, Padres (No. 50 on Top 100; No. 1 on Padres' Top 20): Gyorko has more or less clinched the gig as Opening Day starter at second base, hitting .283 and slugging .547 in 53 at-bats.

Aaron Hicks, OF, Twins (No. 98 on Top 100; No. 6 on Twins' Top 20): Hicks seems to have carried the strides he made last year into Spring Training, hitting .306/.352/.633 in 15 games. He's slowed since a torrid start, but still could be the guy in center for the Twins on Opening Day.

Brandon Maurer, RHP, Mariners (No. 10 on Mariners' Top 20): Forget about Walker, Hultzen or Paxton, this guy has been the most impressive young pitcher in the Mariners' camp, holding opponents to two runs over 15 innings. He's in the hunt for the No. 5 spot in the rotation.

Shelby Miller, RHP, Cardinals (No. 25 on Top 100; No. 2 on Cardinals' Top 20): With Joe Kelly the expected winner of the Cards' final rotation spot, it might be an uphill battle for Miller, but his four shutout innings in his most recent outing, during which he gave up one hit, is making St. Louis' decision much harder.

Yasiel Puig, OF, Dodgers (No. 76 on Top 100; No. 1 on Dodgers' Top 20): A very good argument can be made that he's been the best hitting prospect of the spring (.521 average, .854 slugging). It's a crowded outfield in L.A., but Puig is trying to force his way into the picture.

Bruce Rondon, RHP, Tigers (No. 92 on Top 100; No. 2 on Tigers' Top 20): Though Rondon might be eased into the back of Detroit's bullpen as part of a closer-by-committee approach, he has pitched well enough to get some save opportunities. After struggling early, he's reeled off five straight scoreless outings, the last three hitless, while striking out nine in those five innings.

Trevor Rosenthal, RHP, Cardinals (No. 43 on Top 100; No. 4 on Cardinals' Top 20): Quickly taken out of the mix for the last rotation spot, Rosenthal should stick in the bullpen and has been outstanding since focusing on that role this spring, reeling off five scoreless relief outings in a row.

Oscar Taveras, OF, Cardinals (No. 3 on Top 100; No. 1 on Cardinals' Top 20): Taveras doesn't turn 21 until June, so time is on his side. Still, the best pure hitter in the Minors hasn't been overmatched at all this spring.

Julio Teheran, RHP, Braves (No. 31 on Top 100; No. 1 on Braves' Top 20): Putting a rough 2012 behind him, Teheran has been the best starter in Braves camp and cemented his spot in the rotation to start the season. In 20 innings over five starts, he's allowed three runs on seven hits and six walks while striking out 25.

Christian Yelich, OF, Marlins (No. 13 on Top 100; No. 2 on Marlins' Top 20): There's a reason Miami manager Mike Redmond keeps sending Yelich out there: .364/.451/.818 in 44 at-bats. Give him a little time in the upper levels and he'll be ready.

Down but not out

These are prospects who have been sent to Minor League camps but made impressions.

Javier Baez, SS, Cubs (No. 16 on Top 100; No. 1 on Cubs' Top 20): Before being sent to Minor League camp on March 18, Baez homered four times in 43 at-bats and drew comparisons to Gary Sheffield with his bat speed.

Nick Castellanos, OF, Tigers (No. 21 on Top 100; No. 1 on Tigers' Top 20): Sent down on March 19, Castellanos made it clear that his bat is close to being ready for Detroit by going 9-for-24 with two doubles and a homer. Having shifted from third base last year, he'll continue working on playing left field in Triple-A.

Wil Myers, OF, Rays (No. 4 on Top 100; No. 1 on Rays' Top 20): It's a question of when, not if, Myers gets called up as Tampa Bay manager Joe Maddon came to believe he is a better all-around player than advertised.

Yordano Ventura, RHP, Royals (No. 59 on Top 100; No. 3 on Royals' Top 20): Ventura's electric stuff was the talk of Arizona before he was sent down on March 19. He'll be back as a starter or reliever.

Michael Wacha, RHP, Cardinals (No. 83 on Top 100; No. 6 on Cardinals' Top 20): Before being assigned, all the 2012 first-round Draft pick did was hold opponents to one unearned run in 11 2/3 innings. He could be ready to help before the year is over.

Allen Webster, RHP, Red Sox (No. 71 on Top 100; No. 4 on Red Sox's Top 20): Webster certainly made an impression in his first Red Sox camp, striking out 14 and walking just one over 11 innings before being optioned.

Mike Zunino, C, Mariners (No. 23 on Top 100; No. 3 on Mariners' Top 20): The numbers don't look great offensively, but Zunino didn't get a ton of reps at the plate. Still, scouts were impressed with his all-around game and the other Seattle catchers are merely keeping the spot warm for him.

Jonathan Mayo is a reporter for MLB.com and writes a blog, B3. Follow @JonathanMayoB3 on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.